Self-assembled electrical networks

ABSTRACT

Techniques for self assembly of macro-scale objects, optionally defining electrical circuitry, are described, as well as articles formed by self assembly. Components can be joined, during self-assembly by minimization of free energy, capillary attraction, or a combination.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/909,420, filed Jul. 19, 2001 which claims priority to U.S.provisional application Ser. No. 60/219,570, filed Jul. 20, 2000 andU.S. provisional application Ser. No. 60/226,105, filed Aug. 17, 2000.

FEDERALLY SPONSORED RESEARCH

This invention was sponsored by NSF Grant No. CHE9901358. The governmenthas certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates generally to electrical circuitry, andmore particularly to electrical circuitry formed via self-assembly.

BACKGROUND OF THE INVENTION

Self-assembly is a term used to define the spontaneous association ofentities into structural aggregates. The best-known and mostwell-researched area of self-assembly involves molecular self-assembly,that is, the spontaneous association of molecules, a successful strategyfor the generation of large, structured molecular aggregates.Self-assembly of molecules in solution is described by Whitesides, etal., in “Noncovalent Synthesis: Using Physical-Organic Chemistry to MakeAggregates”, Accts. Chem. Res., 28, 37-44 (1995). See also Philp, etal., Angew. Chem., Int. Ed. Engl., 35, 1155-1196 (1996) for molecularself-assembly. Nature includes examples of molecular self-assemblywhere, in the field of biology, many processes involve interfacialinteractions and shape selectivity to form complex, three-dimensionalstructures.

Self-assembly of molecules can be made to occur spontaneously at aliquid/solid interface to form a self-assembled monolayer of themolecules when the molecules have a shape that facilitates orderedstacking in the plane of the interface and each includes a chemicalfunctionality that adheres to the surface or in another way promotesarrangement of the molecules with the functionality positioned adjacentthe surface. U.S. Pat. No. 5,512,131 and U.S. patent application Ser.Nos. 08/659,537, 08/616,929, 08/676,951, and 08/677,309, andInternational Patent Publication No. WO 96/29629, all commonly-owned,describe a variety of techniques for arranging patterns ofself-assembled monolayers at surfaces for a variety of purposes. Seealso Whitesides, G. M., “Self-Assembling Materials”, ScientificAmerican, 273, 146-149 (1995) for a discussion of self-assembly.

Self-assembly of components larger than molecules is known, for example,self-assembly of bubbles at an air-liquid interface, small spheresself-assembled on surfaces, self-assembly of microspheres viabiochemical attraction between the microspheres, and the like. Yamaki,et al., in “Size Dependent Separation of Colloidal Particles inTwo-Dimensional Convective Self-Assembly” Langmuir, 11, 2975-2978(1995), report “convective self-assembly” of colloidal particles rangingin size from 12 nm to 144 nm in diameter in a wetting liquid film on amercury surface. Size-dependent two-dimensional convective assemblyoccurred, with larger particles being positioned in the center of theaggregate and smaller particles at the periphery. Cralchevski, et al.,in “Capillary Forces Between Colloidal Particles” Langmuir, 10, 23-36(1994), describe capillary interactions occurring between particlesprotruding from a liquid film due to the capillary rise of liquid alongthe surface of each particle. A theoretical treatment of capillaryforces active spheres is presented. Simpson, et al., in “Bubble RaftModel for an Amorphous Alloy”, Nature, 237-322 (Jun. 9, 1972), describepreparation of a two-dimensional amorphous array of bubbles of twodifferent sizes as a model of an amorphous metal alloy. The bubbles wereheld together by a general capillary attraction representative of thebinding force of free electrons in the metal.

U.S. Pat. No. 5,545,291 (Smith) describes assembly of solidmicrostructures in an ordered manner onto a substrate through fluidtransfer. The microstructures are shaped blocks that, when transferredin a fluid slurry poured onto the top surface of a substrate havingrecessed regions that match the shapes of the blocks, insert into therecessed regions via gravity. U.S. Pat. No. 5,355,577 (Cohn) describes amethod of assembling discrete microelectronic or micro-mechanicaldevices by positioning the devices on a template, vibrating thetemplate, and causing the devices to move into apertures. The shape ofeach aperture determines the number, orientation, and type of devicethat it traps.

While self-assembly at the molecular level is relatively well-developed,self-assembly at larger scales is not so well-developed. Many systems inscience and technology require the assembly of components that arelarger than molecules into assemblies, for example, microelectronic andmicroelectrochemical systems, sensors, and microanalytical andmicrosynthetic devices. Photolithography has been the principaltechnique used to make microstructures. Although enormously powerful,photolithography cannot easily be used to form non-planar andthree-dimensional structures, it generates structures that aremetastable, and it can be used only with a limited set of materials.

The fabrication of electronic devices is well established.Microelectronic devices are typically fabricated via photolithography,which is inherently a two-dimensional process. The three-dimensionalinterconnections required in state of the art microelectronics devicestypically are fabricated by the superposition of stacked, parallelplanes, and by their connection using perpendicular vias. While thesearrangements have been very successful, they require numerous designconsiderations ranging from minimization of RC delays due to longinterconnects, to dissipation of heat using cooling channels designedinto three-dimensional structures.

U.S. Pat. No. 5,075,253 (Sliwa) suggests integration of segmentedcircuitry devices into two-dimensional arrangements using capillaryforces at the surface of a floatation liquid.

Commonly owned, co-pending U.S. patent application Ser. No. 08/816,662,filed Mar. 13, 1997 by Bowden, et al., entitled “Self-Assembly of MacroScale Articles”, as well as the following literature references: Bowden,et al. “Self-assembly of mesoscale objects into ordered two-dimensionalarrays”, Science (Washington, D.C.) (1997), 276(5310), 233-235; Terfort,et al., “Three-dimensional self-assembly of millimeter-scalecomponents”, Nature (London) (1997), 386(6621), 162-164; Bowden, et al.,“Mesoscale Self-Assembly: Capillary Bonds and Negative Menisci”, J.Phys. Chem. B (2000), 104(12), 2714-2724; Bowden, et al.,“Molecule-Mimetic Chemistry and Mesoscale Self-Assembly”, Acc. Chem.Res. (2001), 34(3), 231-238; Bowden, et al., “Self-Assembly ofMicroscale Objects at a Liquid/Liquid Interface through LateralCapillary Forces”, Langmuir (2001), 17(5), 1757-1765, describeself-assembly of some electrical components, and self-assembly of somethree-dimensional objects.

While the above and other arrangements are, in some cases, verypromising, it would be desirable to introduce flexibility and varietyinto the possible techniques for fabricating three-dimensionalcircuitry.

SUMMARY OF THE INVENTION

The present invention provides techniques for self-assembly of componentarticles, and articles so assembled.

In one aspect, the invention provides a series of methods. One methodinvolves allowing a first, a second, a third, and a fourth component toassemble in a non-planar arrangement of components, in the absence ofany external net force applied to any of the first, second, third, orfourth components in the direction of any others of the first, second,third, or fourth components. Where each component includes portions ofan electrical circuit, at least one electrical circuit can thereby beformed that traverses at least one portion of each of the first, second,third, and fourth components.

In another aspect, the invention provides a series of articles. In oneembodiment, an article comprises a non-planar assembly of at least afirst, a second, a third, and a fourth component. The components areconstructed and arranged to have the ability, individually, in theabsence of any external net force applied to any of the components inthe direction of any others of the components, to form the assembly. Thefirst, second, third, and fourth components can together define anelectrical circuit that traverses at least one portion of each of thefirst, second, third, and fourth component.

Although electrical circuits are primarily exemplified herein, theinvention is not so limited. The invention relates to methods of formingself-assembled structures and structures so formed regardless of whetherthey include electrical circuits or not.

Other advantages, novel features, and objects of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings, which areschematic and which are not intended to be drawn to scale. In thefigures, each identical or nearly identical component that isillustrated in various figures is represented by a single numeral. Forpurposes of clarity, not every component is labeled in every figure, noris every component of each embodiment of the invention shown whereillustration is not necessary to allow those of ordinary skill in theart to understand the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates, schematically, formation of electrical circuitry onindividual components that are self-assembled to form an assemblyincluding an electrical circuit that traverses each of the components;

FIG. 2 illustrates, schematically, joinder of individual components viamating surfaces; and,

FIG. 3 illustrates, schematically, articles assembled in accordance withthe invention and electrical circuitry defined thereby.

DETAILED DESCRIPTION OF THE INVENTION

Commonly-owned co-pending U.S. patent application Ser. No. 08/816,662,filed Mar. 13, 1997, by Bowden, et al., entitled “Self-Assembly ofMacro-Scale Articles”, as well as the following literature references:Bowden, et al., “Self-assembly of mesoscale objects into orderedtwo-dimensional arrays”, Science (Washington, D.C.) (1997), 276(5310),233-235; Terfort, et al., “Three-dimensional self-assembly ofmillimeter-scale components”, Nature (London) (1997), 386(6621),162-164; Bowden, et al., “Mesoscale Self-Assembly: Capillary Bonds andNegative Menisci”, J. Phys. Chem. B (2000), 104(12), 2714-2724; Bowden,et al., “Molecule-Mimetic Chemistry and Mesoscale Self-Assembly”, Acc.Chem. Res. (2001), 34(3), 231-238; Bowden, et al., “Self-Assembly ofMicroscale Objects at a Liquid/Liquid Interface through LateralCapillary Forces”, Langmuir (2001), 17(5), 1757-1765, are incorporatedherein by reference. Any and all techniques used in any of thesedocuments for self-assembly can be used, alone or in combination, withany aspects of the invention described below, alone or in combination.

The present invention provides techniques for self-assembly ofelectrical circuitry three-dimensionally, rather than two-dimensionally.Individual components of an overall circuit are initially in aseparated, non-interconnected state and, without net external forcesapplied to any of the individual components in a direction of any of theother individual components, are allowed to contact each other and tofasten to each other to form a self-supporting, three-dimensionalelectrical circuit.

A self-supporting electrical circuit, in this context, means anelectrical circuit including at least one electrically conductivepathway that traverses portions of the circuit that had initially beenat least two, individual and separate components. In preferredembodiments, an electrical pathway traverses three or more, orpreferably all portions of a final three-dimensional electricalself-supporting arrangement that had been individual components prior toself-assembly. Portions of individual components, prior toself-assembly, that define an electrically-conductive pathway spanningmultiple components after self-assembly can define any portion, orproportion, of the individual components. That is, an individualcomponent can include a large electrically-conductive component thatdefines a large proportion of the individual component, for examplegreater than fifty percent of the surface area or internal structure. Orthe electrically-conductive portion of the individual components candefine less than forty percent, less than thirty percent, less thantwenty percent, or less than ten percent of the individual component. Inpreferred embodiments, the component includes an electrically-conductiveportion that defines but one of the above percentages or less, theremainder of the component being electrically non-conductive. An exampleof such a component is a polymeric structure including, on one or more(preferably a plurality) of surfaces thereof an electrically-conductivemetal such as copper, or the like. Any of a variety of polymericmaterials can be used as basic component structures.

“Three-dimensional”, in the context of self-assembled structures of thepresent invention, means structures that are arranged from componentsthat form a generally non-planar self-assembled arrangement. Preferably,a final, three-dimensional self-assembled structure is arranged suchthat a single plane can not be arranged in any way so as to contact allcomponents that join to form the three-dimensional structure. Forexample, a generally non-planar, self-assembled arrangement includes onein which a plane can be arranged to intersect first, second, and thirdcomponents that come together to form the structure, but does notintersect a fourth component of the self-assembled structure. Also inpreferred embodiments, at least one component includes at least twosurface contact areas that are not coplanar, and are not parallel, andat each surface contact area a separate component makes contact with andfastens to the surface contact area and defines anelectrically-conductive pathway or pathways traversing the differentcomponents, and, preferably, electrically connecting all componentstogether.

In particularly preferred embodiments a plurality of components areprovided each having at least two surface contact areas, or matingsurfaces, that are essentially flat, at least one component includingthree or more surface contact areas that are essentially flat. In eachcomponent, each surface contact area is preferably non-coplanar with allother surface contact areas and is parallel with respect to no more thanone other surface contact area. The surface contact areas of at leastone of the components define at least three different, non-parallelplanes, and can comprise four, five, or more non-parallel, differentplanes. Examples of shapes of components useful in the invention includepolyhedra. In such arrangements, many components can fasten to a singlecomponent at different surface contact areas, or mating surfaces, and,where this is the case for many of the components, highly-complexstructures can be formed.

Self-assembled structures of the invention are useful for a variety ofpurposes, including light-emitting diodes such as those described below.

The components, and the electrical circuitry associated with thecomponents and with the final, three-dimensional, self-assembledstructure can be of a variety of sizes. The self-assembled structures ofthe invention find particular use at a small scale, where at least oneindividual component includes a maximum dimension of no more than abouttwo centimeters, preferably no more than about one centimeter, morepreferably still no more than about eight millimeters, and in someembodiments, no more than about five millimeters. In preferredembodiments at least two components, or preferably three, four, five,eight, or ten components each include a maximum dimension of one of theabove preferred dimensions and joined together to form at least oneelectrical circuit that traverses at least one portion of thecomponents.

As mentioned, the present invention involves self-assembly of componentsinto three-dimensional, self-supporting structures in the absence ofexternal net force applied. As used herein, “external net force” ismeant to define a non-random force applied to a self-assemblingcomponent, in the direction of a second self-assembling component, for aperiod of time sufficient to cause the components to mate. Examples ofnon-random, external net forces include a mechanical force applied to acomponent selectively, application of an electric or magnetic field to acomponent susceptible to such a field, the use of gravity to causeself-assembly to occur, and the like. Self-assembly can be facilitatedby application to a system of energy that does not constitute anexternal net force, as defined above, for example agitation of a systemallowing random component/component interactions leading toself-assembly as described herein. In another aspect, no energy isapplied to a system of components and self-assembly occurs spontaneouslyover time.

In some embodiments individual components include contact surface areasthat are non-distinguishable by other components, that is, a secondcomponent can contact any of a number of contact surface areas of afirst component with equal likelihood, and equal energy associated withcontact. In other embodiments the first component may include two ormore contact surface areas, but only one of the contact surface areas isconstructed and arranged to mate with a contact surface area of a secondcomponent. That is, two components may each include a plurality ofsurface contact areas, but each may include only one mating surface withrespect to the other component. A “mating surface” in this context is asurface of a component that is shaped in a predetermined manner and/orotherwise adapted to mate selectively with a mating surface of anothercomponent. Mating surfaces also can include a chemical functionalitythat is attractive to its counterpart mating surface, and that does notattract other contact surface areas that are not mating contact surfaceareas. For example, mating contact surface areas may includecomplimentary adhesive, or may each be hydrophobic while other contactsurface areas are hydrophilic, or vice versa. Preferably, matingsurfaces promote self-assembly via reduction of free energy of theoverall system, optionally alone or in combination with factorsdescribed elsewhere herein.

Individual components can be assembled to form an assembly comprising atleast one electrical circuit by allowing them to contact each otherunder conditions that favor the juxtaposition of mating surfacesenergetically, upon random interactions between components. For example,mating surfaces can be rendered hydrophobic, with other surfacesrendered hydrophilic, and in aqueous solution in the presence of randomforces (e.g., random mixing or vibrational agitation), juxtaposition ofthe mating surfaces will be a lower-energy arrangement and will resultafter sufficient random component/component interactions. Alternatively,mating surfaces can be hydrophilic with remainder surfaces hydrophobic,with random interactions carried out in a hydrophobic medium. Those ofordinary skill in the art are aware of techniques for selectivelymodifying specific surface areas to expose a chemical functionality orphysical characteristics different from surrounding areas, and allowingsuch components to self-assemble in an appropriately selected medium, asdescribed in the above-referenced patent application of Bowden, et al.,and literature references of Bowden, et al., Terfort, et al., Bowden, etal., and Bowden, et al., incorporated by reference. This technique canbe used, optionally, in combination with processes based on capillaryinteractions or forces between patterns of features of mating surfaces,such as solder drops (described more fully below).

Electrical circuits result from the provision, on surfaces or withinindividual components, of individual portions of an overall electricalcircuit. Once self-assembly of components occurs in a manner dictated byjuxtaposition of mating surfaces, an overall electrical circuit spanningindividual components results where individual portions of theelectrical circuit are electrically connected to each other uponmatching of mating surfaces of individual components.

The following general exemplary self-assembled electrical circuit willbe described to illustrate one way in which the invention can bemanifested. Those of ordinary skill in the art, upon reading thisdisclosure, will recognize other ways that electrical circuits can becreated, via self-assembly, and the invention is not intended to belimited by the following description.

This example involves the formation of two fundamental classes of 3Delectrical networks—parallel and serial—by self-assembly as a strategyfor fabricating three-dimensional (3D) microelectronic devices. Thebasic component in this exemplary assembly is a polyhedron (a truncatedoctahedron, TO), on whose faces electrical circuits are printed. In theexemplary demonstrations, these circuits include light emitting diodes(LEDs) to demonstrate electrical connectivity and trace the networks.Although not shown, they can also include devices with more complexfunctionality (e.g. processors). The LEDs are wired to patterns ofsolder dots on adjacent faces of the polyhedron. The TO are suspended ina liquid that has approximately the same density as the components thatself-assemble to form the electrical circuit. Self-assembly is carriedout under set conditions that allow the mating surfaces of thecomponents to interact and to fasten to each other irreversibly underthe set conditions. That is, random interactions between the componentsoccur until the mating surfaces contact each other and are in registerwith each other. Once that occurs, without a change in the conditions(i.e., continuing under the set conditions), the components are joinedirreversibly unless significant net forces are applied to one or both ofthe components in a direction that would cause them to separate. Sincethe self-assembly system does not involve such net external forces, butrelies upon random interactions, net forces do not exist that wouldseparate the components. Once the components are joined, conditions canbe changed to further solidify, i.e., render more permanent,interconnects between the components. For example, the temperature ofthe system can be changed after joinder of the mating surfaces to causecomponents of the mating surface to solidify relative to each other. Forexample, the set conditions can define a temperature at which portionsof the mating surfaces under the set conditions (irreversible under theset conditions), the temperature can be reduced to solidify the liquidand further solidify the connection between the mating surfaces. Thisfurther solidification can result in an assembly that is irreversible,i.e. individual components do not become detached from each other, evenin the presence of net external forces that would otherwise cause themto separate. For example, the TO can be suspended in an approximatelyisodense liquid at a temperature above the melting point of the solder(T_(m)˜47° C.), and allowed to tumble gently into contact with oneanother. The drops of molten solder fuse, and the minimization of theirinterfacial free energy generates the forces that assemble the TO intoregular structures.

The function and advantage of these and other embodiments of the presentinvention will be more fully understood from the examples below. Thefollowing examples are intended to illustrate the benefits of thepresent invention, but do not exemplify the full scope of the invention.

EXAMPLES

Processes based on capillary interactions between solder drops have beenused previously to assemble electronic and mechanical structures:examples include “flip-chip” technology (Miller/IBM J. Res. Develop.,239 (May 1969)), and the rotation of parts of microstructures intonon-planar orientations (R. R. A. Syms, E. M. Yeatman, ElectronicsLetters 29, 662 (1993); F. K. Harsh, V. M. Bright, Y. C. Lee, Y., Sens.Actuators A77, 237 (1999)). During assembly, recognition of the patternof dots on one face by that on another orients and registers thepatterns, and results in well-defined pattern of dot-on-dot electricalconnections between different polyhedra. With appropriate designs,self-assembly of polyhedra can generate networks in which the LEDs areconnected either in parallel or in series.

Fabrication: FIG. 1 outlines both the fabrication of the patternedpolyhedra and their self-assembly into 3D structures that includeselectrical networks. (A) An array of the basic pattern of copper dots18, contact pads 28 and wires 19 was defined on a flexiblecopper/polyimide sheet 20 using photolithography and etching. (B)Resulting pattern elements 22 were cut out along the dotted line asshown, (C) glued on the faces of polyhedra 24, and (D) LEDs 26 weremanually soldered on the contact pads. (E) The copper dots and wires onthe TO were coated with solder, and self-assembly 28 of the patternelements occurred in a hot, isodense, aqueous KBr solution, that wasagitated by rotation.

Masters for forming the polyhedra were machined out of aluminum, andmolds were made from these masters using poly (dimethyl siloxane) (PDMSSylgard 184, Dow Corning). Polymeric polyhedra were then cast in thesemolds using a photocurable polyurethane polymer (NOA 73, Norland). Asheet of flexible copper-polyimide composite (Pyralux LF 9110, DuPont)was coated with a photoresist (Microposit, 1813, Shipley) usinghexamethyldimethylsiloxane (HMDS) as a primer. Both were spun on at 4000rpm. After a soft-bake at 115° C. (5 min), this sheet was exposed to UVlight through a negative mask containing an array of the pattern ofconnector dots, contact pads and wires. The exposed photoresist wasdeveloped and the exposed copper was removed by etching with an aqueousferric chloride solution (1.4 g FeCl₃/mL of H₂O). Unexposed photoresistwas removed with acetone. The basic pattern was then cut out manuallyand glued (Krazy glue, Elmer's Products) to the faces of the polyhedra.In the demonstrations of parallel and serial networks, LEDs (BL-HS136,American Bright Optoelectronics Corp.) were manually soldered (RosinCore Solder, Radio Shack, m.p. ˜185° C.) onto the copper contact pads.These soldered regions were coated with a thin impervious layer ofadhesive (CA-50 Gel, 3M) to avoid wetting and cohesion of these regionsduring assembly. The adhesive was allowed to harden completely over 48hours. The polyhedra were then immersed in a bismuth solder (117, SmallParts Inc. m.p. ˜47° C.) which was melted in an aqueous solution ofhydrochloric acid (pH ˜1). The acid dissolved the oxide layer on thecopper and the solder. The solder coated only the exposed copper regionson the polyhedra (dots and wires), but did not wet the polymericsurfaces. The solder-coated polyhedra were allowed to self-assemble inan aqueous KBr solution [density 1.1-1.4 g/cm³, pH 3-4 adjusted withacetic acid (to dissolve oxides on the solder; a function similar tothat of flux in conventional soldering), ˜0.001% (v/v) of soap(Triton-X100, Aldrich, to prevent the formation of bubbles at thesurface of the polyhedra)], in an indented round-bottomed flask, heatedabove the melting point of the solder (˜70° C.) in an oil bath. Theflask was placed horizontally on a rotary evaporator that was rotated at5-20 rpm. All self-assemblies were completed within an hour. Theassemblies were rotated for an average of fifteen minutes after theyformed, at which time the assembly was allowed to cool. The last fifteenminutes may serve to anneal the structure to correct errors in theconnections. On cooling, the molten solder interconnects solidified, andgave the aggregates sufficient strength that they could be manipulated.

Solder patterns: A scheme was used in which LEDs were mounted on thehexagonal faces of the TO, and solder dots were placed on the squarefaces. To maximize the rate of self-assembly, all of the square faces ofthe TO had the same four-fold symmetric pattern of solder dots, defininga mating surface. With this pattern, perfect registration of patterns onjuxtaposed faces occurred in one of four indistinguishable ways; dots onthe patterns that transformed into each other under four-fold rotationalsymmetry were equivalent, and served the same function. On the 3 mm×3 mmsquare face, the width of all of the solder dots was ˜1 mm. Referring toFIG. 2, (A) The widths of all the dots 18 in the patterns used wereapproximately the same, while the width of the wires 19 was muchsmaller. (B) A cross-sectional view (Section XX′ in (A)) of twoassembling faces. The height of the solder coating the wires is ˜15%that on the dots. (C) When the faces connect, the solder dots fuse witheach other, while the wires between them do not touch. (D-E) Theprinciple used to design patterns of solder dots that connect with weaklocal minima. The dotted lines represent the boundaries of theindividual patterns. (D) This pattern—four square dots—can assemble withcomplete overlap of only two of the four dots, and generate a relativelystable but misaligned structure. (E) Complete overlap of individual dotsin this pattern cannot occur unless all the dots are correctly aligneddefining an energy minimum. (F) A pattern comprising dots that can beused for both parallel and serial networks.

A common size was preferred: the solder wetted the copper with awell-defined contact angle, and each drop therefore had the same height.Empirical testing suggested that the optimum distance between adjacentsolder dots was approximately one-half their width. Smaller separationsresulted in electrical shorting between dots due to bridging withsolder; larger separations resulted in misalignment. We designed thepattern of solder dots to give an energy diagram for self-assemblyhaving one large (global) minimum, and relatively weak local minima(FIG. 2, D and E).

Wires: The wires that connect different solder dots electrically on eachTO were fabricated in the same way as the dots. When the patterned TOwere dipped in solder, these wires were also covered with a solderlayer. By making the wires substantially narrower (˜150 μm) than thediameter of the dots (˜1 mm), the height of the solder film on the wireswas limited to ˜15% that on the dots. When the faces self-assembled, thelarger dots fused into connections, but the smaller wires did not touchand fuse (FIG. 2,C). It was, as a result, unnecessary to insulate thewires to prevent shorting, even when they crossed on juxtaposed faces oftwo TO.

Architecture: These examples demonstrate, by self-assembly in 3D,networks that are widely used in current 2D integrated circuittechnology. In these systems, pins on processors belong to one of threegroups: buses (A₁′, . . . , A_(n)′; driving voltage, clock), inputs(I₁′, . . . , I_(m)′), and outputs (O₁′, . . . , O_(m)′). Bus linesconnect processors in parallel (A_(j)′⇄A_(j)″, j=1, . . . ,n) whileoutputs of one processor connect serially to inputs of adjacentprocessors and, vice versa (O_(j)′⇄I_(j)″, j=1, . . . ,m).

In the pattern of solder dots shown in FIG. 2, F, the five dots (1, 2,5, 8 and 11) lie on reflection axes; and provide two sets of dots (basedon four fold rotational symmetry; {1} and {2, 5, 8 and 11}). Duringself-assembly, dots from one set on a TO connect to dots from the sameset on another TO. These dots are used for parallel or bus lineconnections. The other dots: {3, 6, 9 and 12} and {4, 7, 10 and 13} formtwo sets based on their four-fold rotational symmetry. Dots from thefirst set are related to dots from the second set by reflectionsymmetry. On assembly, dots from one set on a TO (e.g. outputs from oneprocessor) connect to those from the other set on another TO (e.g.inputs to a second processor). These dots are used for serial, I/Oconnections.

Parallel Networks (Buses): FIG. 3 (A-D) shows the realization of a 3Dnetwork with parallel connectivity, using self-assembly. In theassembled aggregate, LEDs on one TO connected to those on the adjacentTO in parallel, along three orthogonal directions. The fidelity of theinterconnects was visualized by lighting up the LEDs connected inparallel in the assembly. This self-assembled, 3D parallel networkmimicked bus lines in circuits in which a number of electricalcomponents are powered by the same common wires.

Serial Networks (I/O connections): FIG. 3 (E-I) shows the realization ofa 3D network with serial connectivity, using self-assembly. (A) Thebasic pattern of copper dots 18, wires 19 and contact pads 28 used. Thesolder dots included dots 2, 5, 8, 11 and 1 (FIG. 2, F), that lie on theaxes of symmetry of the square face. Two electrically isolated wiresconnected the two sets. A LED 26 was soldered on the contact padsbetween the wires using a polarity in which the cathode is connected tothe wire between the dots 2, 5, 8 and 11, and the anode was connected tothe wire between dots 1. (B) The pattern was glued on the TO 24 in sucha way that the copper dots covered two opposite square faces, while thetwo wires ran across the two hexagonal faces between them. There arethree LEDs 26 on each TO 28. (C) A photocopy of a photograph of theself-assembled aggregate on a penny (to provide a size prospective). Twoelectrically isolated pairs of wires were connected to a battery tovisualize electrical continuity in the aggregate: The illuminated loopcomprises six LEDs 26 that consist of two sets of LEDs (three in eachset) that connect in parallel. (D) An electrical circuit diagram showingthe parallel network formed. The circles 30 show the position of thecenters of each of the 12 TOs. The half circles 32 represent connectiondots at the assembling faces of two TO. The LEDs 26 are shown as well.Assembly results in the formation of 16 pairs of wires, which include offour, six and six pairs in each of the three dimensions. The six LEDsthat are lit up are highlighted by black squares. (E-I) A self-assembled2×2×3 aggregate containing 12 TO and demonstrating serial connectivity.(E) The pattern of solder dots containing a pair of the dots 3, 6, 9, 12and 4, 7, 10, 13 (FIG. 2, F) that do not lie on the axes of symmetry ofthe square face. Dots 4, 6 and 10, 12 are connected to each other, whiledots 3, 9 and 7, 13 are wired to contact pads. (F) The terminals of asingle LED are directly soldered across two contact pads, and a wire issoldered in a way that connects the third contact pad to one of one ofthe terminals of the LED, using a polarity in which the anode of the LEDconnects to dots from the set 3, 9 and the cathode connects to dots fromthe set 7, 13. (G) A pattern TO prior to assembly. The TO contains eightLEDs, one on each of its hexagonal faces, with the six square facescovered with the pattern of connector dots. (H) A 2×2×3 self-assembledaggregate with 96 LEDs (with a penny for perspective). The 12 polyhedraare labeled a through l. The eight LEDs on each TO are labeled α throughθ. The LEDs on different TO connect to each other in serial loops ofvarious sizes. The loops were traced by powering pairs of leads:Individual loops range in size from those containing two LEDs to onethat contains ten LEDs; the latter is illuminated. (I) The circuitdiagram of the serial network aggregate shown in (H). The circles 40represent individual polyhedra, and the triangles 42 represent the LEDs.The 96 LEDs (eight on each polyhedron) connect cathode to anode in allloops. The lines and diodes represent the loop containing ten LEDs thatis lit up using a battery (H).

In order to reduce the number of circuits that would be formed (and ofLEDs required to check their electrical connectivity), and to minimizethe geometrical problems of packing the LEDs in the arrays, only four ofthe dots (“active” dots) in the solder pattern ({3, 9} {and {7, 13})were wired to LEDs. The other four dots ({6, 12} and {4, 10}) wereconnected to each other (“passive” dots). The active and passive dotshad two-fold symmetry, while the global pattern on individual connectordots on the assembling square faces had four-fold symmetry. Thisdifference in symmetry resulted in the formation of a stochastic networkon self-assembly (if a deterministic network were required, all the dots({3, 6, 9 and 12} and {4, 7, 10 and 13}) would need to be connected toLEDs). There are three types of connections which result from overlap ofdots at each assembling face (a) connections between LEDs on differentTO, involving only active dots with a probability of one-fourth (b)connections between LEDs on the same TO, involving both active andpassive dots with a probability of one-half and (c) connectionscontaining no LEDs, involving only passive dots with a probability ofone-fourth. The important feature of the assembled 3D network was thatthe cathode of one LED always connected to the anode of another LEDacross the assembling faces. This connectivity was visualized bylighting up the serial loops in the assembly; FIG. 3H shows one loopcontaining ten LEDs. In bipolar, random system, the probability of theanode connecting to the cathode is one-half. For ten LEDs to form afunctional serial loop, the probability would be ½⁹ or 1/512. The serialconnectivity in this architecture mimicked I/O connections in integratedcircuits.

This system—using capillary forces between patterns of solder drops toform interconnections between different electrical components in3D—provides a foundation for the self-assembly of 3D, multicomponentelectronic devices. The 3D assemblies can be designed to be porous: Thisporosity may allow for cooling fluid to be pumped through theassemblies. The shape of the distribution of solder dots on theassembling faces raises interesting questions regarding the“recognition” of one pattern by another.

Although these examples demonstrate parallel and serial connectivityseparately, it is possible to extend these ideas to more complexnetworks involving different combinations of parallel and serialconnections. The LEDs in our demonstrations represents simple bipolarelectronic devices; in order to fabricate 3D computational devices,elements of digital logic (e.g. five-pin single logic gates (five-pin,single logic gates are part of the Little Logic™ line of products soldby Texas Instruments) can be incorporated into the 3D assemblies. Thestrategy of self-assembling networks facilitates the formation of a highdegree of interconnection between individual processing elements indetermining ways.

Those skilled in the art would readily appreciate that all parameterslisted herein are meant to be exemplary and that actual parameters willdepend upon the specific application for which the methods and apparatusof the present invention are used. It is, therefore, to be understoodthat the foregoing embodiments are presented by way of example only andthat, within the scope of the appended claims and equivalents thereto,the invention may be practiced otherwise than as specifically described.Specifically, those of ordinary skill in the art will recognize, or beable to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. Such equivalent are intended to be encompassed by the followingclaims.

In the claims, all transitional phrases such as “comprising”,“including”, “carrying”, “having”, “containing”, “involving”, and thelike are to be understood to be open-ended, i.e. to mean including butnot limited to. Only the transitional phrases “consisting of” and“consisting essentially of”, respectively, shall be closed orsemi-closed transitional phrases as set forth in the United StatesPatent Office Manual of Patent Examining Procedures, section 2111.03.

1-9. (canceled)
 10. An article comprising a non-planar assembly of at least a first, a second, a third, and a fourth component that together define an electrical circuit traversing at least one portion of each of the first, second, third, and fourth components, wherein the first, second, third, and fourth components are constructed and arranged to have the ability, individually, in the absence of any external net force applied to any of the first, second, third, or fourth components in the direction of any others of the first, second, third, or fourth components, to form the assembly.
 11. An article as in claim 10, the component articles each having a dimension of at least about 250 nm.
 12. An article as in claim 10, the component articles each having a dimension of at least about 500 nm.
 13. An article as in claim 10, comprising a self-assembled composite of at least five separate component circuit articles.
 14. An article as in claim 10, wherein at least one of the separate component circuit articles has a dimension of at least 150 nm.
 15. An article as in claim 10, wherein at least two of the component articles have dimensions of at least one micron.
 16. An article as in claim 10, wherein at least one of the first, second, third, or fourth components is rotationally symmetric.
 17. An article, comprising: an electrical circuit, formed via self-assembly, having integrated circuit connectivity, the electrical circuit comprising at least first, second, and third components intersected by a first plane, and fourth, fifth, and sixth components intersected by a second plane that is not coplanar with the first plane, wherein a single plane cannot be arranged in any way so as to contact each of the first, second, third, fourth, fifth, and sixth components, the electrical circuit traversing at least one portion of each of the first, second, third, fourth, fifth, and sixth components.
 18. The article of claim 17, wherein each of the first, second, third, fourth, fifth, and sixth components comprises a diode.
 19. The article of claim 17, wherein each of the first, second, third, fourth, fifth, and sixth components comprises a processor.
 20. The article of claim 17, wherein each of the first, second, third, fourth, fifth, and sixth components comprises an electrical device.
 21. An article, comprising: an electrical circuit, formed via self-assembly, having integrated circuit connectivity, the electrical circuit comprising at least first, second, and third components intersected by a first plane, and fourth, fifth, and sixth components intersected by a second plane that is not coplanar with the first plane, wherein a single plane cannot be arranged in any way so as to contact each of the first, second, third, fourth, fifth, and sixth components, the electrical circuit traversing at least one portion of each of the first, second, third, fourth, fifth, and sixth components, the electrical circuit having a porous structure, wherein at least some pores are defined between components, each of the first, second, third, fourth, fifth, and sixth components comprising a surface contact area for connection to another component, each surface contact area exhibiting rotational symmetry and a local free energy minima configuration that enhances alignment of the surface contact area to the surface contact area of another component and the electrical connectors thereon, and each surface contact area comprising a first set of electrical connectors and a second set of electrical connectors such that any two of the first, second, third, fourth, fifth, and sixth components are joinable in a plurality of electrically indistinguishable configurations wherein, in each of the indistinguishable configurations, at least one of the first set of electrical connectors on the first component joins to at least one of the second set of electrical connectors on the second component and at least one of the second set of electrical connectors on the first component joins to at least one of the first set of electrical connectors on the second component.
 22. The article of claim 21, wherein each surface contact area is constructed such that, in at least two different rotational orientations of two of the components relative to each other, around an axis passing through surface contact areas of each at which they are joined, a functionally identical electrical connection between the two components is formed; and wherein each of the components comprises a plurality of surface contact areas and is constructed such that it is able to connect to another component via either of at least two of its surface contact areas in an electrically and structurally indistinguishable manner.
 23. The article of claim 21, wherein the electrical connectors of each surface contact area are arranged on the surface contact area in a rotationally symmetric manner; and wherein each of the components comprises a plurality of surface contact areas and is constructed such that it is able to connect to another component via either of at least two of its surface contact areas in an electrically and structurally indistinguishable manner.
 24. The article of claim 21, wherein at least some pores have a shape sufficient to allow a fluid to pass therethrough.
 25. The article of claim 21, further comprising a cooling fluid within at least some of the pores.
 26. The article of claim 21, wherein the first set of electrical connectors on the first component and the second set of electrical connectors on the second component are able to join to form a parallel circuit.
 27. The article of claim 21, wherein the first set of electrical connectors on the first component and the second set of electrical connectors on the second component are able to join to form a series circuit.
 28. The article of claim 21, wherein the first set of electrical connectors forms an I/O connection.
 29. The article of claim 21, wherein the first set of electrical connectors forms a bus. 